This invention relates to position-sensing apparatus and to a probe for sensing the position of an object in such apparatus.
It is known in numerically controlled machine tools to provide an automatic tool change mechanism adapted to connect either a tool or a probe to the operating spindle of the machine, the probe being required for the purpose of measuring a workpiece machined by the tool. When a tool is connected to the spindle the latter is then rotated to perform a cutting operation but when a probe is connected to the spindle the latter is held against rotation as is required for a probing operation.
The probe comprises an assembly including means defining an electric circuit, a battery for energising said circuit, and means for changing the state of the circuit responsive to the probe attaining a sensing relationship with the workpiece. It is also known to provide the assembly with a switch for switching the battery on or off, the switch being operated to switch the battery on by engagement of a switch operating member with the spindle when the probe is connected to the spindle, and the battery being automatically switched off when the switch operating member becomes disengaged from the spindle as a result of the probe being removed from the spindle. Thus the probe is armed only when it is connected to the spindle and battery power is saved in this way. However, there is still a waste of power because the probe is not in use all the time it is connected to the spindle. It is an object of this invention to reduce or overcome this difficulty.